Refrigerator and operating method of the same

ABSTRACT

When a Stirling refrigerating engine for cooling a refrigerator starts, an operation is performed such that a gas-phase fluid flowing through a natural circulation circuit on a high temperature side attains a temperature higher than that in a normal operation. More specifically, the Stirling refrigerating engine operates with a piston drive speed higher than a normal speed, or a fan motor arranged for a condenser on the high temperature side stops. Thereby, a gas/liquid coexistent refrigerant in a high temperature side evaporator attains a pressure higher than a normal pressure. Thereby, a liquid phase fluid in a forced-circulation circuit on a high temperature side also attains a pressure higher than a normal pressure so that bubbles produced in the liquid phase fluid disappear, and a circulation pump can start.

TECHNICAL FIELD

The present invention relates to a refrigerator having a cooling space for cooling stored goods as well as an operating method of the same.

BACKGROUND ART

General refrigerators have widely employed vapor compression refrigerating engines. The vapor compression refrigerating engine utilizes condensation and evaporation of a flon gas to achieve a low temperature. Since the flon gas has neither flammability nor explosibility, and has low corrosivity, it can be used very readily as a refrigerant. However, the flon gas has a high chemical stability. Therefore, when the flon gas is released into an atmosphere, it reaches the stratosphere to destroy the ozone layer. In recent years, therefore, specified flon (i.e., chlorofluorocarbon) and alternative flon have been used, and the production of the flon gas has been restricted on a worldwide basis.

In recent years, therefore, attention has been given to a Stirling refrigerating engine as a refrigeration technique that can be substituted for the vapor compression refrigerating engine using the flon gas as the refrigerant. The Stirling refrigerating engine is configured to reciprocate a piston and a displacer with an arbitrary phase difference by an external power such as a motor. This operation repetitively compresses and expands a working medium. Consequently, a cold head and a warm head are formed. The cold head achieves a low temperature.

The Stirling refrigerating engine can use, as the working medium, a gas of helium, hydrogen, nitrogen or the like that does not adversely affect the global environment.

Patent Document 2: Japanese Patent Laying-Open No. 11-166784

Patent Document 3: Japanese Patent Laying-Open No. 11-211325

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In a refrigerator provided with the Stirling refrigerating engine described above, the cold head takes the heat from an inner space of the refrigerator, and the warm head releases the heat as waste heat so that the inner space can be cooled without using the flon gas.

However, the refrigerator provided with the Stirling refrigerating engine suffers from a problem similar to that of the conventional refrigerators. More specifically, the foregoing refrigerator suffers from a problem that dews are formed on portions (e.g., a portion around a door packing and an outer wall surface of the refrigerator) that are cooled to a lower temperature than a surrounding environment by an inner cold air when the humidity in the surrounding environment is high.

Such a refrigerator is already proposed that prevents the dew formation by an electric heater heating portions on which the dew formation may occur. However, this structure suffers from a problem of increase in electric power consumption.

For overcoming the above problems, the inventors and others have made study of a refrigerator that can prevent formation of dews on the outer wall, and can perform drain processing. This refrigerator is configured such that a liquid portion of a refrigerant used for cooling a warm head of a Stirling refrigerating engine is forcedly led to a dew formation preventing pipe arranged near an outer wall or a drain processing pipe arranged at a lower portion of the refrigerator.

The above dew formation preventing pipe is filled with a liquid phase fluid such as water. Therefore, a gas phase for externally releasing a heat and a liquid phase for preventing dew formation are present in a two-phase state. A circulation pump is used for forcedly circulating the liquid phase fluid.

In the above forced circulation, when a surrounding temperature rises when a circulation pump stops for a predetermined time, the temperature of the liquid phase fluid also rises with it. This may gasify a part of the liquid phase fluid remaining in the dew formation preventing pipe. Bubbles generated by gasifying the liquid phase fluid remain in the liquid phase dew formation preventing pipe and/or in the circulation pump. This results in a problem that the circulation pump cannot appropriately circulate the liquid phase fluid.

The invention has been made in view of the above problems, and it is an object of the invention to provide a refrigerator and an operating method thereof that can eliminate bubbles formed in a liquid phase dew formation preventing pipe when the refrigerator stops its operation for a long time, and thereby can overcome the problem that a liquid phase circulation pump cannot appropriately circulate the liquid phase fluid during the operation of the refrigerator.

Means for Solving the Problems

A refrigerator according to the invention is as follows:

A refrigerator includes a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling the cooling room and a warm head releasing heat caused by the generation of the cold air; a liquid phase circulation circuit connected to the warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in the liquid phase circulation circuit and circulating the liquid phase fluid; and pressurizing means capable of pressurizing the liquid phase fluid.

According to this structure, the pressurizing of the liquid phase fluid by the pressurizing means eliminates bubbles that appeared in the liquid phase fluid when the operation of the refrigerator stops for a long time. Consequently, such a problem is prevented that the liquid phase circulation pump runs idle, and the liquid phase fluid does not circulate through the liquid phase circulation circuit when the operation of the refrigerator starts.

The refrigerator may include a circulation circuit connecting the warm head to a condenser for liquidizing a gas phase fluid vaporized by the heat provided from the warm head.

In an operation method of the invention, the refrigerator described above applies a high pressure higher than a pressure applied in a normal operation to the gas phase fluid after the start of the operation until the liquid phase circulation pump appropriately circulates the liquid phase fluid.

In the above method, the pressurizing of the liquid phase fluid eliminates the bubbles that occur in the liquid phase fluid when the operation of the refrigerator stops for a long time. Consequently, such a problem is prevented that the liquid phase circulation pump runs idle, and the liquid phase fluid does not circulate through the liquid phase circulation circuit when the operation of the refrigerator starts.

The foregoing high pressure may be produced by operating the refrigerating machine to raise the temperature of the warm head above the temperature in a normal operation. The foregoing high pressure may be produced by operating the heating means arranged independently of the warm head to raise the temperature of the gas phase fluid above a normal temperature.

For executing the above method, the refrigerator may include heating means arranged in the circulation circuit and capable of pressurizing the gas phase fluid to apply a pressure to the liquid phase fluid through a gas-liquid separator. This pressurizing means may be achieved by controlling the warm head to attain a temperature higher than that in the normal operation, and may also be achieved by heating means that has a heat source independent of the warm head and can apply heat to the liquid phase fluid and/or the gas phase fluid.

Further, the refrigerator includes a control device controlling the refrigerating machine, and the control device executes control of performing a high-speed operation of a piston of the refrigerating machine or control of increasing a stroke of a piston of the refrigerating machine such that the warm head of the refrigerating machine attains a temperature higher than that in a normal operation after the start of operation of the refrigerator until the liquid phase circulation pump appropriately circulates the liquid phase fluid.

According to another aspect of the invention, a refrigerator includes a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling the cooling room and a warm head releasing heat caused by the generation of the cold air; a liquid phase circulation circuit connected to the warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in the liquid phase circulation circuit and circulating the liquid phase fluid; and a control device controlling the refrigerating machine and the liquid phase circulation pump.

In the above structure, the control device may start the operation of the liquid phase circulation pump on condition that a predetermined time has elapsed after the refrigerating machine started the operation. Thereby, during a period of the predetermined time, a pressure is applied to the liquid phase fluid owing to the rising of temperature of the warm head of the refrigerating machine so that the liquid phase fluid pressurizes bubbles. Consequently, the bubbles remaining in the liquid phase circulation circuit can be eliminated. Thereafter, the liquid phase circulation pump starts. Accordingly, it is possible to suppress generation of noises caused by the bubble elimination that occurs in the liquid phase circulation circuit due to the rapid start of the circulation pump.

In the above structure, the control device may increase the output of the liquid phase circulation pump on condition that a predetermined time has elapsed after the refrigerating machine started the operation, and thereby can reduce a flow velocity of the liquid phase fluid circulating through the liquid phase circulation circuit immediately after the start of the refrigerating machine until the normal operation is performed. Consequently, it is possible to reduce noises caused by the bubble elimination that occurs in the liquid phase circulation circuit due to the rapid start of the circulation pump.

According to still another aspect of the invention, a refrigerator includes a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling the cooling room and a warm head releasing heat caused by the generation of the cold air; a liquid phase circulation circuit arranged along an inner surface of a casing, connected to the warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in the liquid phase circulation circuit and circulating the liquid phase fluid; a control device controlling the refrigerating machine and the liquid phase circulation pump and; and a temperature sensor measuring a temperature of the surface of the casing or a temperature of the liquid phase circulation circuit. The control device starts the liquid phase circulation pump, or increases the output of the liquid phase circulation pump on condition that the temperature sensed by the temperature sensor lowered.

According to the above structure, the liquid phase circulation pump can start after the temperature of the liquid phase fluid lowers and the bubbles in the liquid phase circulation circuit disappear owing to the condensation. Therefore, it is possible to suppress generation of noises caused by the bubble elimination that occurs due to the rapid start of the circulation pump.

It is desirable that the foregoing refrigerator further includes a humidity sensor measuring a humidity near a predetermined position. It is also desirable that the control device decreases an output of the liquid phase circulation pump from the current output, or stops the circulation pump when the humidity measured by the humidity sensor attains the predetermined value or more.

According to the above structure, the temperature of the liquid phase fluid in the circulation pipe rises with the temperature of the warm head, and therefore a dew point of an atmosphere around the liquid phase circulation circuit rises so that dew formation near the liquid phase circulation circuit can be suppressed.

According to yet another aspect of the invention, a refrigerator includes a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling the cooling room and a warm head releasing heat caused by the generation of the cold air; a liquid phase circulation circuit connected to the warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in the liquid phase circulation circuit and circulating the liquid phase fluid; a radiator for lowering a temperature of the warm head; a radiator fan arranged near the radiator; and a control device controlling the refrigerating machine, the liquid phase circulation pump and the radiator fan. Before the liquid phase circulation pump starts after starting the refrigerating machine, the control device stops the radiator fan or drives the radiator fan with a power smaller than that used after starting the liquid phase circulation pump.

According to the above structure, the rising of the temperature of the warm head can raise the temperature of the liquid phase fluid before the start of the liquid phase circulation pump, as compared with the operation after the start of the liquid phase circulation pump. Thereby, the pressure of the liquid phase fluid eliminates bubbles in the liquid phase circulation pump. Thereafter, the circulation pump starts. Consequently, it is possible to suppress generation of noises caused by the elimination of the bubbles in the liquid phase circulation pump.

EFFECTS OF THE INVENTION

The invention can eliminate the bubbles that occur in the liquid phase fluid when the operation of the refrigerator stops for a long time. Consequently, such a problem is prevented that the liquid phase circulation pump runs idle, and the liquid phase fluid does not circulate through the liquid phase circulation circuit when the operation of the refrigerator starts.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing a schematic structure of a refrigerator of an embodiment.

FIG. 2 shows a structure of piping of the refrigerator of the embodiment.

FIG. 3 is a block diagram for illustrating a control device.

FIG. 4 illustrates a gas-liquid separator arranged around a cold head.

FIG. 5 illustrates an operation temperature of a circulation pump during an operation in a refrigerator operation method of the embodiment.

FIG. 6 is a flowchart illustrating start processing of the refrigerator of the first embodiment.

FIG. 7 illustrates a refrigerator provided with heating means different from a warm head of the refrigerator.

FIG. 8 is a flowchart illustrating start processing of a second embodiment.

FIG. 9 is a flowchart illustrating start processing of a third embodiment.

DESCRIPTION OF THE REFERENCE SIGNS

1 refrigerator, 10 housing, 11, 12 and 13 cooling room, 14, 15 and 16 heat-insulating door, 17 packing, 18 shelf, 19 machine room, 20 duct, 21 cold air outlet, 22 fan, 30 Stirling refrigerating engine, 40 low temperature side circulation circuit, 41 low temperature side condenser, 42 low temperature side evaporator, 50 high temperature side natural circulation circuit, 51 high temperature side evaporator, 52 high temperature side condenser, 60 high temperature side forced circulation circuit, 61 circulation pump, 62, 63 and 64 dew formation preventing pipe, 70 electric heater, 80 dew formation sensing portion, 81 wall surface humidity sensor, 82 wall surface temperature sensor, 90 control device, 110 radiator fan

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the invention will now be described with reference to the drawings.

First Embodiment

FIG. 1 is a cross section showing a schematic structure of a refrigerator of this embodiment. FIG. 2 shows a piping structure of the refrigerator of this embodiment. A refrigerator 1 is aimed at food storage, and includes a housing 10 of a heat-insulating structure. Three cooling rooms or compartments 11, 12 and 13 are formed at different levels in housing 10, respectively.

Cooling rooms 11, 12 and 13 have openings on a front side (left side in FIG. 1) of housing 10, respectively. These openings are closed by openable heat-insulating doors 14, 15 and 16, respectively. Heat-insulating doors 14, 15 and 16 are provided at their rear surfaces with packings 17 surrounding the openings of cooling rooms 11, 12 and 13, respectively. Shelves 18 suitable for types of foods to be stored are appropriately arranged in cooling rooms 11, 12 and 13.

A cooling system and a heat radiating system that include a Stirling refrigerating engine 30 as a main component are arranged over upper, rear and lower surfaces of housing 10. A machine room 19 is arranged at a corner between the upper and rear surfaces of housing 10, and Stirling refrigerating engine 30 is arranged in machine room 19. A part of Stirling refrigerating engine 30 forms a cold head during an operation. A wall surface temperature sensor 82 and a wall surface humidity sensor 81 are arranged in the wall on the rear side (right side in FIG. 1) of the cooling rooms. Wall surface temperature sensor 82 can measure the temperature of a portion neighboring to the rear surface of the cooling room and also neighboring to a dew formation preventing pipe 62 to be described later. Wall surface humidity sensor 81 can measure the humidity of a portion neighboring to the rear surface of the cooling room and also neighboring to dew formation preventing pipe 62 to be described later. Information obtained by wall surface temperature sensor 82 and wall surface humidity sensor 81 is transferred via signal lines to a control device 90 to be described later.

A low temperature side condenser 41 is attached to the foregoing cold head. A low temperature side evaporator 42 is arranged on a rear side of cooling room 13. Low temperature side condenser 41 and low temperature side evaporator 42 are connected together via a refrigerant pipe, and both form a low temperature side circulation circuit 40. Low temperature side circulation circuit 40 is filled with a natural medium such as CO₂, which transfers cold by low temperature side evaporator 42 and low temperature side condenser 41.

A duct 20 is arranged within housing 10 for distributing a cold air obtained by low temperature side evaporator 42 to cooling rooms 11, 12 and 13. Duct 20 is provided at appropriate positions with cold air outlets 21 communicating with cooling rooms 11, 12 and 13. Blowers or fans 22 are arranged inside duct 20 for forcedly discharging the cold air.

Although not shown, a duct of collecting the air from cooling rooms 11, 12 and 13 is arranged inside housing 10. This duct has an opening located under low temperature side evaporator 42, and the air to be cooled is supplied to low temperature side evaporator 42 as indicated by an arrow B of broken line in FIG. 1.

Another part of Stirling refrigerating engine 30 forms a warm head when it operates. A high temperature side evaporator (warm head) 51 is attached to the warm head. A temperature sensor 55 is attached to high temperature side evaporator 51 as shown in FIG. 2. A high temperature side condenser 52 releasing the heat to an outside environment as well as a radiator fan 110 are arranged on an upper surface of housing 10 (see FIG. 1). High temperature side evaporator (warm head) 51 and high temperature side condenser 52 are connected together via refrigerant piping to form a high temperature side natural circulation circuit 50. Radiator fan 110 rotates to form an air flow, which promotes heat exchange between high temperature side condenser 52 and the outside air.

High temperature side natural circulation circuit 50 is filled with a natural medium of water (including aqueous solution) or hydrocarbon, and the natural medium naturally circulates through high temperature side natural circulation circuit 50.

High temperature side evaporator (warm head) 51 is also connected to a high temperature side forced circulation circuit 60. High temperature side forced circulation circuit 60 has a circulation pump 61 forcedly circulating the refrigerant, and also has pipes 62, 63 and 64 for preventing dew formation. The refrigerant pipe that forms dew formation preventing pipes 62, 63 and 64 is partially located in the openings of cooling rooms 11, 12 and 13.

The heat of the refrigerant is applied to the vicinities of the openings where the dews are likely to occur (i.e., to the portions near the contact portion between packing 17 and housing 10, i.e., the boundary region between the outer and inner spaces), and thereby the dew formation is prevented. An electric heater 70 that can be energized to generate heat is attached to a portion where the dew formation may occur but high temperature side forced circulation circuit 60 cannot be arranged due to a reason, e.g., relating to manufacturing.

Description will now be given on the operation of refrigerator 1 having the above structure. When Stirling refrigerating engine 30 is driven in refrigerator 1 having the above structure, the temperature of the cold head lowers. Therefore, low temperature side condenser 41 is cooled to condense the refrigerant kept therein.

The refrigerant condensed by low temperature side condenser 41 flows into low temperature side evaporator 42 through low temperature side circulation circuit 40. The refrigerant flowing into low temperature side evaporator 42 is evaporated by the heat of the air flowing outside low temperature side evaporator 42, and lowers the surface temperature of low temperature side evaporator 42.

Therefore, the air passing by low temperature side evaporator 42 becomes cold, and flows into cooling rooms 11, 12 and 13 through cold air outlets 21 of duct 20 so that the temperatures of cooling rooms 11, 12 and 13 lower. Thereafter, the air in cooling rooms 11, 12 and 13 returns to the vicinity of low temperature side evaporator 42 through the duct (not shown) owing to the air flow caused by the rotation of fans 22.

The refrigerant evaporated by low temperature side evaporator 42 returns to low temperature side condenser 41 via low temperature side circulation circuit 40, which condenses the refrigerant by taking the heat. The heat exchange operation described above is repeated.

As illustrated in FIG. 2, when the heat caused by the operation of Stirling refrigerating engine 30 and the heat collected from the inside of the refrigerator by the warm head are released as waste heat from the warm heat. Therefore, high temperature side evaporator (warm head) 51 is heated to evaporate the refrigerant flowing therein.

The refrigerant that is evaporated by high temperature side evaporator (warm head) 51 and is in the gas phase state flows through high temperature side natural circulation circuit 50 into high temperature side condenser 52 arranged in an upper position. The air that is supplied by radiator fan 110 from the outside into high temperature side condenser 52 takes the heat from the refrigerant flowing into high temperature side condenser 52, and thereby condenses it. The refrigerant condensed by high temperature side condenser 52 returns to high temperature side evaporator (warm head) 51 via high temperature side natural circulation circuit 50, and receives the heat to evaporate again. The foregoing heat exchange operation is repeated.

The liquid phase refrigerant contained in the refrigerant that is saturated inside high temperature side evaporator (warm head) 51 is forcedly circulated by circulation pump 61 through high temperature side forced circulation circuit 60, and is supplied into dew formation preventing pipes 62, 63 and 64. Therefore, the refrigerant thus supplied heats the portions near the openings of cooling rooms 11, 12 and 13 by its heat.

Owing to the above structure, the portions near the openings, i.e., the portions where the dews are liable to occur can be kept at a temperature higher than a dew point without requiring a wasteful electric power, and the dew formation can be prevented. There are portions where the dew may be formed but high temperature side forced circulation circuit 60 cannot be arranged. When electric heater 70 is energized, it can keep such portions at a temperature higher than the dew point, and thereby can prevent the dew formation thereon.

As shown in FIG. 3, refrigerator 1 of this embodiment has a dew formation detecting portion 80 that determines, based on the temperature and humidity of the ambient air, the degree of possibility of the dew formation at the vicinities of the openings, and also has control device 90 that controls radiator fan 110, circulation pump 61 and electric heater 70 based on a result of the determination by dew formation detecting portion 80.

This control device is configured to control a circulation rate of the refrigerant in high temperature side forced circulation circuit 60 and a quantity of the heat released from high temperature side natural circulation circuit 50 according to the degree of possibility of the dew formation. Further, control device 90 is supplied with a signal indicating the temperature measured by temperature sensor 55 that is employed for measuring the temperature of high temperature side evaporator (warm head) 51. Control device 90 is configured to control the operation of Stirling refrigerating engine 30 based on the signal thus supplied.

More specifically, when control device 90 determines based on the result of detection of dew formation detecting portion 80 that the possibility of the dew formation near the opening is high, it starts the operation of circulation pump 61 and the energizing of electric heater 70. When control device 90 determines that the possibility of the dew formation is low, it stops the operation of circulation pump 61 and the energizing of electric heater 70.

Owing to the above structure, unnecessary heating is not effected on the outer wall surface of the refrigerator when the possibility of dew formation near the opening is low. Therefore, a thermal load on the inside of the refrigerator can be suppressed, and the power consumption can be reduced. For example, when the ambient temperature is high and the ambient humidity is low, the load required for the cooling increases, and the warm head attains a high temperature.

However, the foregoing control reduces the circulation quantity of the refrigerant in high temperature side forced circulation circuit 60. Consequently, the dew formation can be appropriately prevented without heating the outer wall surface of the refrigerator. The employment of the foregoing structure reduces the operation time of circulation pump 61, i.e., a machine element that is relatively liable to go wrong, and therefore can contribute to improvement of the reliability of the refrigerator.

When control device 90 determines based on the result of detection of dew formation detecting portion 80 that the possibility of the dew formation near the opening is high, it performs another control, simultaneously with the foregoing control, to reduce the quantity of air supplied from radiator fan 110 (i.e., the quantity of released heat of high temperature side natural circulation circuit 50), and to cause a difference of a predetermined value or more between the surface temperature of the warm head and the ambient temperature. The temperature difference of the predetermined value or more was obtained in advance by experiments so that the refrigerant flowing through dew formation preventing pipes 62, 63 and 64 may attain the temperature equal to or higher than the ambient temperature.

Owing to the above structure, even when the load on Stirling refrigerating engine 30 is small (e.g., when an ambient temperature is low and an ambient humidity is high), the cooling temperature of high temperature side forced circulation circuit 60 is maintained at a predetermined value or more. Consequently, dew formation preventing pipes 62, 63 and 64 can always function.

As shown in FIGS. 2 and 3, it is desirable that dew formation detecting portion 80 has wall surface humidity sensor 81 that measures wall surface humidity at the position (e.g., around dew formation preventing pipes 62, 63 and 64) where the dew formation is liable to occur to a relatively high extent. In this structure, it is desirable that control device 90 determines that the possibility of dew formation is high when the relative humidity is, e.g., 90% or more, and determines that the possibility of dew formation is low when the relative humidity is lower than 90%.

Owing to the above structure, control device 90 can directly determine the possibility of dew formation according to the relative humidity near the outer wall surface of the refrigerator. Consequently, the dew formation can be quickly detected by the simple structure.

Wall surface temperature sensor 82 and wall surface humidity sensor 81 provide the temperature information and humidity information obtained at the vicinity of dew formation preventing pipe 62 to control device 90. Based on the temperature information and the humidity information, control device 90 can control radiator fan 110, electric heater 70, circulation pump 61 and Stirling refrigerating engine 30.

Referring to FIGS. 4 to 6, description will now be given on a manner of pressurizing a gas phase fluid for eliminating bubbles that occurred in the liquid phase fluid in the dew formation preventing pipes according to the embodiment.

As can be seen from FIG. 4, a liquid phase is present on the lower side of high temperature side evaporator 51 of the refrigerator already described, and a gas phase is present on the upper side so that high temperature side evaporator 51 functions as a gas-liquid separator. Therefore, bubbles generated on the liquid phase side generally move upward and are discharged to the gas phase side. Consequently, a state where no gas (or substantially no gas) is present is kept on the liquid phase side.

However, when the refrigerator stops its operation for a long term, the ambient temperature may rise to vaporize a part of the liquid phase fluid so that the bubbles may occur in dew formation preventing pipes 62, 63 and 64. When a large amount of bubbles occur, the liquid phase fluid does not circulate through dew formation preventing pipes 62, 63 and 64 even when the refrigerator operates, i.e., even when circulation pump 61 operates. Therefore, the dew formation prevention cannot be executed.

In the operation method of the refrigerator of the embodiment, therefore, when the refrigerator starts the operation, it enters such an operation state that a piston reciprocates at a higher speed than a normal speed. Thus, by reciprocating the piston faster than the normal speed, high temperature side evaporator (warm head) 51 attains a higher temperature than the normal operation in the heat exchange cycle. For example, in the refrigerator having high temperature side evaporator (warm head) 51 that attains 38° C. in the normal operation, the piston operates fast to raise the temperature of high temperature side evaporator (warm head) 51 to 50° C. until circulation pump 61 starts as illustrated in FIG. 5. The temperature is gradually lowered after circulation pump 61 started. When high temperature side evaporator (warm head) 51 attains to 38° C., the normal operation starts.

As described above, when bubbles are present in dew formation preventing pipes 62, 63 and 64 at the start of the refrigerator, the refrigerator operates to set high temperature side evaporator (warm head) 51 to the temperature higher than that in the normal operation so that the bubbles in dew formation preventing pipes 62, 63 and 64 are compressed by the pressure of the gas in high temperature side natural circulation circuit 50 that is the pipe on the gas phase side. Thus, the pressure of the gas in high temperature side natural circulation circuit 50 increases the pressure of the fluid on the liquid phase side. Thereby, the gas in the liquid phase changes into a liquid, and the bubbles disappear. Thereafter, circulation pump 61 starts so that it can operate successfully. The foregoing method prevents the occurrence of the disadvantage at the start of the operation

FIG. 6 is a flowchart for illustrating the start processing of the refrigerator of the first embodiment of the invention. In the start operation of the embodiment, it is first determined in S1 whether the start switch of Stirling refrigerating engine 30 is turned on or not. When the start switch of the refrigerating engine is not turned on in S1, the start processing is not performed, and the processing ends as it is. When the start switch of the refrigerating engine is turned on in S1, processing in S2 is executed.

In S2, it is determined whether the stop time of circulation pump 61 is equal to or longer than a predetermined time or not. A timer measures the stop time of circulation pump 61 from the point of time when circulation pump 61 stopped. The data about this stop time have been successively stored in a RAM (Random Access Memory) in control device 90.

In S2, when the stop time of circulation pump 61 is shorter than the predetermined time, the start processing is not performed, and the processing ends as it is. More specifically, when the stop time of circulation pump 61 is shorter than the predetermined time, the probability that the bubbles have occurred in dew formation preventing pipes 62, 63 and 64 is extremely low, and therefore the start processing is not performed. However, instead of measuring the stop time of circulation pump 61, the following structure and manner may be employed. Flow meters measuring flow rates of the liquid phase fluid in dew formation preventing pipes 62, 63 and 64 are arranged in dew formation preventing pipes 62, 63 and 64, respectively. Values of the flow meters are read after a certain time from the start of circulation pump 61, and it is determined whether circulation pump 61 is operating or not. Thereby, the determination whether the start processing is to be performed or not is performed.

Then, in S3, a drive velocity V of the piston of Stirling refrigerating engine 30 is set to an initial value. This drive speed V of the piston is larger than that in the normal operation. Then, in S4, the piston is driven at drive speed V higher than the normal operation. Thereby, the piston is driven faster than the normal operation so that high temperature side evaporator (warm head) 51 of the refrigerator attains a higher temperature than the normal operation.

Then, in S5, it is determined whether such a state is attained or not that high temperature side evaporator (warm head) 51 is at a higher temperature than the normal operation and the elapsed time of the operation in this high-temperature state is equal to or longer than a predetermined time. When the predetermined time has not elapsed in S5, the operation of operating the piston faster than the normal operation is repeated in S4. When high temperature side evaporator (warm head) 51 operates at a higher temperature than the normal operation for the predetermined time or more in S5, the processing is then executed in S6.

In S6, circulation pump 61 operates. Before this stage, circulation pump 61 does not operate (except for the case where the flow meters are employed) for the following reasons. When Stirling refrigerating engine 30 stops for the predetermined time, there is a high possibility that the bubbles have occurred in dew formation preventing pipes 62, 63 and 64, and therefore there is a high possibility that circulation pump 61 runs idle when it operates before S6.

Then, in S7, it is determined whether the temperature of high temperature side evaporator (warm head) 51 has lowered or not. When the liquid phase fluid starts to circulate through dew formation preventing pipes 62, 63 and 64, the heat of the hot portion is transferred to dew formation preventing pipes 62, 63 and 64 so that the temperature of high temperature side evaporator (warm head) 51 lowers. The fact that the temperature of the hot portion has lowered means that circulation pump 61 starts to circulate the liquid phase fluid in dew formation preventing pipes 62, 63 and 64. When the temperature of high temperature side evaporator (warm head) 51 has not lowered the predetermined temperature or more, the processing of stopping circulation pump 61 is executed in S8. The fact that the temperature of high temperature side evaporator (warm head) 51 has not lowered means that the liquid phase fluid in dew formation preventing pipes 62, 63 and 64 has not yet circulated. In the structure having the flow meters measuring the flow rates of the liquid phase fluid, the determination whether the liquid phase fluid has circulated or not may be performed in S7 based on the flow rates of the liquid phase fluid.

Then, in S9, the value of V is set to ((initial value)×1.2). Thereby, the piston operates in S4 at a further high drive speed that is 1.2 times larger than last drive speed V of the piston. The steps S4-S7 are repeated. When the temperature of high temperature side evaporator (warm head) 51 has lowered a predetermined value in S7, it is determined that the liquid phase fluid in dew formation preventing pipes 62, 63 and 64 started the circulation, and Stirling refrigerating engine 30 starts the normal operation in S10. Thereafter, the start processing ends.

In the foregoing embodiment, the control is performed to achieve the piston speed (frequency) larger than that in the normal operation for setting high temperature side evaporator (warm head) 51 to a higher temperature than the normal operation. However, control may be performed to achieve such a state immediately after the start of Stirling refrigerating engine 30 that the piston speed (frequency) is equal to that in the normal operation but a piston stroke is larger than that in the normal operation. This control can likewise set high temperature side evaporator (warm head) 51 to the higher temperature than the normal operation. Therefore, even when the control is executed to achieve the larger piston stroke than the normal operation immediately after the start of Stirling refrigerating engine 30, circulation pump 61 can be driven after eliminating the bubbles in dew formation preventing pipes 62, 63 and 64.

In this specification, the time of the normal operation means the timing of performing the operation after the start of Stirling refrigerating engine 30 while stopping circulation pump 61 or suppressing the output of circulation pump 61.

Second Embodiment

A refrigerator of a second embodiment will now be described. The refrigerator of the second embodiment has substantially the same structure as that of the first embodiment already described. Therefore, the second embodiment will be described only in connection with portions different from those in the first embodiment.

In the refrigerator of the first embodiment, the additional and independent heating device is not employed, and the operation method of the refrigerating machine, i.e., freezing machine is changed to apply the pressure to the gas phase fluid flowing in high temperature side natural circulation circuit 50. Instead of these structure and method, the second embodiment employ heating means (e.g., heater) 100 that can apply heat to the gas phase fluid flowing through high temperature side natural circulation circuit 50, as specifically illustrated in FIG. 7. By operating this heating means 100, it is possible to heat and thereby pressurize the gas phase fluid flowing in high temperature side natural circulation circuit 50. Thereby, it is possible to eliminate the bubbles in the liquid phase fluid remaining in high temperature side forced circulation circuit 60.

Instead of heating means 100 shown in FIG. 7, the refrigerator may employ pressurizing means such as a pump that can apply a pressure to the gas phase. This manner can likewise eliminate the bubbles in the liquid phase fluid remaining in high temperature side forced circulation circuit 60. Consequently, the effect similar to that already described can be achieved.

The refrigerator of the second embodiment is substantially the same as that of the first embodiment. However, as shown in FIG. 7, the refrigerator of this embodiment differs from that of the first embodiment in that heating means 100 that can heat the gas phase fluid flowing in high temperature side natural circulation circuit 50 is arranged in the pipe passing the fluid from high temperature side condenser 52 of high temperature side natural circulation circuit 50 to high temperature side evaporator 51. Further, control device 90 is configured to heat the gas phase fluid by heating means 100 based on the information sent from temperature sensor 55 that indicates the temperature of high temperature side evaporator (warm head) 51.

Start processing of the refrigerator of the second embodiment will now be described.

In the start processing of the refrigerator of this embodiment, as illustrated in FIG. 8, it is first determined in S11 whether the start switch of the refrigerating machine is on or not. When the start switch of the refrigerating machine is not on in S11, the start processing ends. When the start switch of the refrigerating machine is on in S11, it is determined in S12 whether the stop time of the circulation pump is equal to or longer than a predetermined time or not.

In S12, when the stop time of the circulation pump is shorter than the predetermined time, the start processing ends. In S12, when the stop time of the circulation pump is equal to or longer than the predetermined time, the processing is executed in S13. The steps in S11 and S12 are substantially the same as those in S1 and S2 of the start processing in the first embodiment.

Then, in S13, the temperature to be compared with the temperature of high temperature side evaporator (warm head) 51 is set to the reference value of T. In S14, processing for heating by heating means 100 is performed. Then, in S15, it is determined whether such a situation is satisfied or not that the temperature of high temperature side evaporator (warm head) 51 is equal to or higher than foregoing reference value T and a duration of reference value T is equal or longer than a predetermined time, e.g., of 5 minutes.

When it is determined in S15 that the temperature of high temperature side evaporator (warm head) 51 equal to or higher than reference value T has not been kept for the predetermined time or more, the processing in step S14 continues. When it is determined in S15 that the temperature of high temperature side evaporator (warm head) 51 equal to or higher than reference value T has been kept for the predetermined time or more, the processing in step S16 is executed. In S16, circulation pump 61 operates to execute the processing. In S17, it is determined whether the temperature of high temperature side evaporator (warm head) 51 lowers below reference value T or not. The processing in S17 is completely the same as that in S7 of the first embodiment.

When it is determined in S17 whether the temperature of high temperature side evaporator (warm head) 51 has not lowered below reference value T, processing is performed in S18 to stop circulation pump 61. In S19, reference value T of high temperature side evaporator (warm head) 51 is set to a new reference value (T+5) raised, e.g., by 5 degrees. In next step S14, the temperature higher by 5 degrees than that in the last determining processing is handled as the reference value, and it is determined whether the temperature of high temperature side evaporator (warm head) 51 is higher than the reference value or not. In this manner, steps S14-S17 are repeated.

When circulation pump 61 operates and the temperature of high temperature side evaporator (warm head) 51 has lowered below the predetermined temperature in S17, it is determined that the bubbles in dew formation preventing pipes 62, 63 and 64 disappear and the liquid phase fluid starts to flow in dew formation preventing pipes 62, 63 and 64. Thereby, processing is performed in S20 to stop the heating by heating means 100 (heater). Thereafter, the normal operation starts in S21.

The foregoing embodiment employs such a manner that heating means 100 for heating the gas phase fluid flowing through high temperature side natural circulation circuit 50 eliminates the bubbles in the liquid phase fluid flowing in high temperature side forced circulation circuit 60. However, such a manner may be employed that a pump is arranged for forcedly pressuring the gas phase fluid flowing in high temperature side natural circulation circuit 50, and the pressurized gas phase fluid eliminates the bubbles in the liquid phase fluid flowing in high temperature side forced circulation circuit 60. In this case, it is desired that the refrigerator has pressure measuring means (e.g., pressure sensor) that senses the pressure of the gas phase fluid flowing through high temperature side natural circulation circuit 50, and control device 90 receives the measured value obtained by the pressure measuring means, and controls the pressurizing means (e.g., pump) based on the received signal.

Third Embodiment

A third embodiment of the invention will now be described. The refrigerator of this embodiment has substantially the same structure as the refrigerators of the first and second embodiments. Therefore, the following description will be given on only the portion of this embodiment different from the first and second embodiments.

The start processing performed by control device 90 of Stirling refrigerating engine 30 of the third embodiment will be described with reference to a flowchart of FIG. 9.

In the start processing, it is first determined in S21 whether a switch of the freezing machine, i.e., Stirling refrigerating engine 30 is on or not. When the start switch of the refrigerating machine is not on in S21, processing in S33 is executed. When the start switch of Stirling refrigerating engine 30 is on in S21, processing in S22 is executed. In S22, Stirling refrigerating engine 30 starts the operation. Then, in S23, the output of circulation pump 61 is set to 0 or P₁. Thereafter, a rotation speed of radiator fan 110 is set to 0 or V₁.

In S25, a timer starts. Then, in S26, it is determined whether the foregoing timer determines the elapsing of a predetermined time or not. When the timer does not determine the elapsing of the predetermined time, it continues the time measurement. When the timer determines the elapsing of the predetermined time in S26, it is reset in S27, and processing in S28 is executed.

In S28, a value of T1 of wall surface temperature sensor 82 is obtained. Then, a value T2 of wall surface temperature sensor 82 is obtained again in S29. Thereafter, a difference between values T₂ and T₁ of the wall surface temperature sensor is calculated in S30. Then, the difference (T₂−T₁) is compared with a predetermined value K in S30. When the difference (T₂−T₁) is smaller than predetermined value K in S30, the processing in S29 and S30 is repeated. When the difference (T₂-T₁) is equal to or larger than predetermined value K in S30, the processing in S31 is repeated.

In S31, processing is performed to start circulation pump 61 or to increase the output of circulation pump 61 further from P₁. Then, in S32, control device 90 further increases the rotation speed of radiator fan 110 further from V₁.

Thereafter, a value H of wall surface humidity sensor 81 is obtained. Then, in S34, it is determined whether value H of wall surface humidity sensor 81 is equal to or larger than 90% or not. When it is determined in S34 that value H of wall surface humidity sensor 81 is equal to or larger than 90%, processing in S35 is executed. However, when it is determined in S34 that value H of wall surface humidity sensor 81 is smaller than 95%, the processing in S35 is not performed, and processing in S36 is performed. In S35, control device 90 lowers the output of circulation pump 61, or stops circulation pump 61. In S36, the control starts to perform the normal operation by Stirling refrigerating engine 30.

According to the start processing of the Stirling refrigerating engine of this embodiment, the processing in S25-S27 is performed to determine whether the predetermined time has elapsed after the turn-on of the start switch of Stirling refrigerating engine 30. When the predetermined time has elapsed after the start of Stirling refrigerating engine 30, the processing is performed in S31 to start circulation pump 61 or to increase the output of circulation pump 61. Therefore, when circulation pump 61 is not operating, the temperature of high temperature side evaporator (warm head) 51 rises so that the temperature of the liquid phase fluid (refrigerant: water) in dew formation preventing pipes 62, 63 and 64 rises immediately after the start of operation of Stirling refrigerating engine 30. Thereby, the temperature of the liquid phase fluid (refrigerant: water) in dew formation preventing pipe 62 rises to increase the pressure of the liquid phase fluid. Consequently, the bubbles remaining in the liquid phase fluid are compressed to disappear. Control device 90 has stored the values of foregoing predetermined time and the foregoing output of circulation pump 61 which were obtained in obtained by experiments.

In S28-S30, a comparison is made between the initial value of the detected temperature of wall surface temperature sensor 82 and the value of the temperature of wall surface temperature sensor 82 detected after elapsing of the predetermined time, and it is determined that the value of the detected temperature of wall surface temperature sensor 82 has lowered the predetermined temperature from the initial temperature. After this determination or confirmation, the processing is performed in S31 to start circulation pump 61 or to increase the output of circulation pump 61. Therefore, after the temperature of the liquid phase fluid (refrigerant: water) in dew formation preventing pipe 62 measured by wall surface temperature sensor 82 lowered the predetermined temperature after the start of Stirling refrigerating engine 30, the operation of circulation pump 61 starts, or the output of circulation pump 61 increases. Thus, the cooling space is cooled to cause lowering of the temperature of the wall surface, and thereby the liquid phase fluid (refrigerant: water) in dew formation preventing pipe 62 lowers so that condensation occurs to eliminate the bubbles remaining in dew formation preventing pipe 62. Thereafter, the processing is performed to start circulation pump 61, or to increase the output of circulation pump 61. Consequently, it is possible to suppress noises that occur when the bubbles in dew formation preventing pipes 62, 63 and 64 are rapidly compressed due to the rapid start of rotation of circulation pump 61. Control device 90 has stored the values of foregoing predetermined temperature K and the foregoing output of circulation pump 61 which were obtained by experiments.

In the foregoing example, the processing in S25-S27 and the processing in S28-S30 are both performed. However, even in a refrigerator performing only the processing in S25-S27 or the processing in S28-S30, it is possible to suppress noises that occur when the bubbles in dew formation preventing pipe 62 disappear due to the rapid operation of circulation pump 61.

After the processing in S25-S30 ends, the rotation speed of radiator fan 110 increases in S32. Thus, rotation speed V₁ of radiator fan 110 increases only in such a state that the bubbles remaining in dew formation preventing pipes 62, 63 and 64 have probably disappeared. Conversely, immediately after the start of Stirling refrigerating engine 30, the rotation speed of radiator fan 110 is smaller than that attained after the start of circulation pump 61. In this state, the heat exchange performance of high temperature side condenser 52 is low. Therefore, immediately after start of Stirling refrigerating engine 30, the temperature of the liquid phase fluid (refrigerant: water) remaining in dew formation preventing pipe 62 is higher than that attained after the start of circulation pump 61. Consequently, the pressure is applied to the liquid phase fluid in circulation pipe 61 to eliminate the bubbles. As described above, the rotation speed of radiator fan 110 that is attained immediately after the start of Stirling refrigerating engine 30 is controlled to be smaller than that attained immediately after the start of circulation pump 61, and this control can likewise suppress the noises that occur due to the disappearance of bubbles remaining in dew formation preventing pipe 62. Control device 90 has stored the value of rotation speed V₁ of radiator fan 110 that was obtained in advance by experiments under the predetermined conditions.

In S33-S35, the determination about the lowering of output of circulation pump 61 or the stop of circulation pump 61 is performed depending on whether wall surface humidity sensor 81 exhibits the predetermined value or not. Thus, the large output of circulation pump 61 prevents the temperature of the liquid phase fluid in dew formation preventing pipes 62, 63 and 64 from lowering below the ambient atmosphere temperature. Consequently, such a situation is prevented that the temperature of the atmosphere near dew formation preventing pipes 62, 63 and 64 as well as the neighboring wall becomes excessively low to increase the humidity of the atmosphere to 100% or more. Thus, the dew formation on the wall surface of the refrigerator is prevented.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

1. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit and circulating said liquid phase fluid; and pressurizing means capable of pressurizing said liquid phase fluid.
 2. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit and circulating said liquid phase fluid; a circulation circuit connecting said warm head to a condenser for liquidizing a gas phase fluid vaporized by the heat provided from said warm head; and pressurizing means capable of pressurizing said liquid phase fluid.
 3. The refrigerator according to claim 1 or 2, wherein said pressurizing means is configured to perform the pressurizing by applying heat to said liquid phase fluid and/or said gas phase fluid from said warm head.
 4. The refrigerator according to claim 1 or 2, wherein said pressurizing means is heating means having a heat source independent of said warm head and being capable of applying heat to said gas phase fluid from said heat source.
 5. A method of operating a refrigerator including: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit and circulating said liquid phase fluid; and a circulation circuit connecting said warm head to a condenser for liquidizing a gas phase fluid vaporized by the heat provided from said warm head, wherein said liquid phase fluid is pressurized by applying a pressure higher than a pressure applied in a normal operation to said gas phase fluid after the start of the operation of said refrigerator until said liquid phase circulation pump appropriately circulates said liquid phase fluid.
 6. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit and circulating said liquid phase fluid; a circulation circuit connecting said warm head to a condenser for liquidizing a gas phase fluid vaporized by the heat provided from said warm head; and a control device controlling said refrigerating machine, wherein said control device executes control of performing a high-speed operation of a piston of said refrigerating machine or control of increasing a stroke of a piston of said refrigerating machine such that said warm head of said refrigerating machine attains a temperature higher than that in a normal operation after the start of operation of said refrigerator until said liquid phase circulation pump appropriately circulates said liquid phase fluid.
 7. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit (60) and circulating said liquid phase fluid; and a control device controlling said refrigerating machine and said liquid phase circulation circuit, wherein said control device starts an operation of said liquid phase circulation pump or increases the output of said liquid phase circulation pump on condition that a predetermined time has elapsed after said refrigerating machine started an operation.
 8. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a dew formation preventing pipe arranged along an inner surface of a casing, connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit including said dew formation preventing pipe, and circulating said liquid phase fluid; a control device controlling said refrigerating machine and said liquid phase circulation pump; and a temperature sensor measuring a temperature of the surface of said casing or a temperature of said liquid phase circulation pipe, wherein said control device starts an operation of said liquid phase circulation pump or increases the output of said liquid phase circulation pump on condition that the temperature sensed by said temperature sensor lowered.
 9. A refrigerator comprising: a cooling room for accommodating a target to be cooled; a refrigerating machine having a cold head generating a cold air for cooling said cooling room and a warm head releasing heat caused by the generation of said cold air; a liquid phase circulation circuit connected to said warm head and passing a liquid phase fluid; a liquid phase circulation pump arranged in said liquid phase circulation circuit and circulating said liquid phase fluid; a radiator for lowering a temperature of said warm head; a radiator fan arranged near said radiator; and a control device controlling said refrigerating machine, said liquid phase circulation pump and said radiator fan, wherein before said liquid phase circulation pump starts after starting said refrigerating machine, said control device stops said radiator fan or drives said radiator fan with a power smaller than that used after starting said liquid phase circulation pump. 